I have built two 260 Rifles, one a VZ24 Mauser with Douglas factory long chambered and blued barrel 10" twist.
Another, 260 on a commercial Mauser with a Shilen stainless match barrel in 9" twist.

Neither shot well enough to compete for hunting privileges against what ever 7mmRemMag I built that year.

But in Sept 2015 a 6.5-06 I built with Shilen select match stainless barrel with 8" twist on a Dumoulin Mauser was getting good groups at 600 yards. I shot a couple deer in 2015 with it.

I am sure there is nothing wrong with the 260 cartridge, the out of control variables are my fault, but I just wanted to share my anecdotes.